New-Tech Europe Magazine | July 2016 | Digital edition

A46E_6cmx23cm_A45.qxd 7/14/16 1:31 PM Page 1

currents are effectively suppressed by connecting bypass capacitors between each power line of the switching power supply and ground. These power lines may be at the input and/or output of the switching power supply. Further suppression of common mode currents can be achieved by adding a pair of coupled choke inductors in series with each main power feed. The high impedance of the coupled choke inductors forces common mode currents through the bypass capacitors. Radiated EMI Radiated EMI can be suppressed by reducing RF impedance and reducing the antenna loop area. This is achieved by minimizing the enclosed loop area formed by the power line and its return path. The inductance of a printed circuit board track can be minimized by making it as wide as possible and routing it parallel to its return path. Similarly, because the impedance of a wire loop is proportional to its area, reducing the area between the power line and its return path will further reduce its impedance. Within printed circuit boards this area can be best reduced by placing the power line and return path one above the other on adjacent printed circuit board layers. Reducing the loop area between a power line and its return path not only reduces the RF impedance, but it also limits the effectiveness of the antenna because the smaller loop area produces a reduced electromagnetic field. Furthermore, a ground plane located on the outer surfaces of the printed circuit board significantly suppresses radiated EMI, particularly if located directly below the noise-generating source.

And to further reduce radiated noise, metal shielding can be utilized, placing the noise-generating source within a grounded conductive housing, and interfacing to the clean outside environment is via in-line filters. Common mode bypass capacitors would also need to be returned to ground on the conductive housing. System-Level EMI Mitigation Techniques Although most switching supplies are designed to meet applicable EMI standards as stand-alone modules, the system itself needs be designed to generate a minimum EMI profile to meet regulatory standards. Specific areas in the system design that are candidates for EMI mitigation practices include the signal lines, printed circuit boards (PCB), and solid state components. Summary Switching power supplies generate EMI because of their inherent design. Domestic and international regulatory bodies regulate these emissions through promulgation of rules and standards such as the FCC Part 15 rules and the CISPR 22 standard. Power modules are one of many components within a system and EMI requirements, both radiated and conductive, apply to an overall electronic system. Since the EMI requirements apply to the overall system, significant effort must be expended on system design to limit noise. Further information on EMI mitigation in power modules, including an application note, is available from the ac-dc power supplies and dc-dc converters pages of the CUI website.

DC-3 Series

DC-1 Series

HiQP Series

ALL MODELS AVAILABLE WITH EXPANDED OPERATING TEMPERATURES SELECTED MILITARY SCREENING CUSTOM DESIGNS • 3.3 -300 VDC regulated isolated outputs • Up to 50 watts, single and dual outputs • Thru hole and terminal strip models HiQP Series • 125-475 VDC input voltage range • 24-200 VDC regulated isolated outputs • Up to 50 watts output power • 2.50” X 1.55” X 0.50” encapsulated package • DC-DC CONVERTERS NEW! ! HIGH INPUT VOLTAGES UP TO 900 VDC. DC-1 Series • 120-370 VDC input voltage range • 5-300 VDC regulated isolated outputs • Up to 300 watts output power • 4.5” X 2.5” X 0.50” encapsulated package DC-3 Series • 300-900 VDC input voltage range • For full characteristics of these and the entire PICO product line, see PICO’s Full line catalog at www.picoelectronics.com

Pico Representatives Germany ELBV/Electronische Bauelemente Vertrieb E-mail: info@elbv.de Phone: 0049 89 4602852 Fax: 0049 89 46205442 England Ginsbury Electronics Ltd. E-mail: rbennett@ginsbury.co.uk Phone: 0044 1634 298900 Fax: 0044 1634 290904 PICO ELECTRONICS, Inc.

New-Tech Magazine Europe l 25